Articles of manufacture can be formed of a virtually infinite number of product materials, for example: polymers, metals, ceramics, pulp, foodstuffs, or other natural or synthetic materials. Solidifiable product materials which are susceptible of being transported in a manufacturing process in a liquid, molten, or semi-solid form are conventionally shaped in injection molding or die casting operations. Such shaped articles comprise polymer, metal, ceramic, pulp, and food products for consumer, commercial, or industrial needs. To meet these product needs, manufacturers have developed injection molding molds and die casting dies which commonly contain multiple product cavities, i.e. multi-impression or family molds. Multi-impression tooling is used to produce a plurality of essentially the same products in a single shot. On the other hand, family mold tooling is used to produce different products in the same shot. Both multi-impression and family systems are formed in tooling whereby a product material flowing into the tool in a liquid, molten, or semi-solid state can be directed through a series of channels into many cavities at once, rather than only one cavity at a time. Multi-impression and family tools, therefore, allow for many products to be made in a single shot, which lowers the cost to produce the products. Moreover, the use of such tools lowers the cost of the tools themselves because less tools are needed overall to produce a given amount of product in a fixed amount of time. Where the cost of producing products is thereby lowered, consumers and industry may see a benefit in the form of lower market prices of such products.
There is, however, a problem with multi-impression and family mold tools regarding the mold filling. All cavities in a given tooling may not be made equal, i.e. there may be volumetric or geometric differences between cavities which will affect the rate at which a cavity can be filled. During the filling process, the volumetric flow rate of the product material entering an easier-to-fill cavity will be higher because the product material will naturally take the path of least resistance. Thus the easier-to-fill cavity can experience over-packing, i.e. too much product material. On the other hand, a harder-to-fill cavity may experience short shots, i.e. the product cavity was not fully filled. When these problems occur, the multi-impression or family tooling may be said to be out of balance. This means that the product material is not flowing in a balanced way to each cavity in the multi-impression or family tooling. A balanced tooling is one where each cavity in the multi-impression or family tooling is conditioned to receive a sufficient mass of product material so that both short shots and over-packing are avoided.
Conventional tooling provides channel shut-off flow valves located in the channels where the product material must flow. Channel shut-off flow valves have two modes of operation, namely, non-variable "on" and "off" modes. Channel shut-off flow valves do not otherwise modulate the material flow or vary product material conditions such as pressure, mass flow rate, or volumetric flow rate. Such channel shut-off flow valves, when in the off mode, block any and all flow to a product cavity. When in the on mode, such shut-off flow valves are fixed in a non-variable, open position. Such a shut-off flow valve is disclosed in U.S. Pat. No. 4,909,725.
Tooling has been developed to attempt to control product material flow to cavities for the purpose of balancing a family mold tool. An article appearing on pages 68-70 of the December, 1995, issue of INJECTION TOOLING magazine entitled: "Balanced Runners in a Family Mold" describes such tooling. The tooling described therein uses gate openings and "channels", i.e. runners, to define a specialized runner/gate system. The runner/gate system comprises runners and gates of various sizes or shapes for the purpose of controlling the filling of a product cavity. Theoretically, smaller gate openings and runners will increase resistance to the flow of the product material to a product cavity at the end of the runner. The relatively smaller gate openings and runners are formed in the family mold tooling such that they lead to a relatively easier-to-fill cavity. In this way, during a shot of product material, the mass or volumetric flow rate is relatively slowed to the easier-to-fill cavity. Consequently, during the same shot, the product material is forced to go toward the harder-to-fill cavity so that it fills up. According to the foregoing, filling of cavities may be controlled, and the family mold tooling may thereby be balanced, by fixing the sizes and shapes of the runner/gate system.
However, in order for the gate openings and runners to be properly sized and shaped, engineers must utilize a computer program so that mathematical calculations can be performed which will define the parameters of the runner/gate system. Once the calculations are believed to be correct, engineering drawings are prepared, and the drawings are used by machinists to make tooling in a tooling shop. At the shop, the runners and gates are permanently cut into the steel of the tooling to define the runner/gate system. The tooling is then put through a start-up conditioning cycle for a given product material, i.e. the tooling is fine tuned, and is then put to the test in the factory. If the runner/gate system, when in actual use in the factory, does not result in acceptable product quality, the tooling must be scrapped or sent back to the shop for further work. Moreover, if a different product material is used in the family mold tooling, the material may have physical characteristics which require another conditioning cycle. This is a time consuming and expensive procedure which may result in lost manufacturing time and higher tooling costs. Consequently, the manufacturer's product costs may rise and consumers may pay higher market prices for the products they need.
In light of the foregoing, what is needed is tooling having a means of controlling the filling of a product cavity, which is suitable for use in either a multi-impression or family tooling application, but which keeps production and tooling costs to a minimum.